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Progressive substitution of Cu for Al in UCu 4+ x Al 8 −x yields as increasing compression of the unit cell. This results in a reduction of the Neel temperature from ifT N = 42 K for x = 0 to ifT N = 15 K for x = 1.0. No magnetic ordering is found for x ⩾ 1.5. Rather the T -dependence of the resistivity shows a maximum in the range 6 to 15 K and indicates the formation of a Kondo-lattice state. The latter is characterized by heavy fermions (γ( T a0)≅0.8 J/K 2 mol for x = 1.75).

Human basic fibroblast growth factor (bFGF) was produced from recombinant Escherichia coli by high-cell-density cultivation. In order to develop a purification strategy for large-scale purification, chromatographic sorbents with different anionic functional groups were compared in terms of selectivity for bFGF and stability under cleaning in place (CIP) conditions. Heparin-Sepharose CL-6B, Fractogel EMD-SO3- 650 (S) and SP-Sepharose (high performance) were found suitable for this purpose with decreasing selectivity in that order. Each sorbent was treated eight times under CIP conditions employing both 0.2 and 1.0 M NaOH, in order to study modifications of these sorbents. Heparin-Sepharose displayed more than 50% loss of capacity after the first CIP treatment and decreasing selectivity with each cycle. Both cation exchangers displayed almost constant results regarding selectivity and capacity. The Fractogel EMD-SO3- exhibited only slightly lower selectivity for bFGF than Heparin-Sepharose and the highest capacity of all sorbents tested. Agglomeration of bFGF at low salt concentrations was a serious problem. By direct application of pooled fractions from Fractogel EMD-SO3- onto Heparin-Sepharose a highly pure product was obtained; however, the recovery after Heparin-Sepharose was only 30%.

We report the preparation of polycrystalline samples with nominal composition (Bi 1-x Pb x ) 2 Sr 2 Ca 2 Cu 3+y O 10-δ with 0 ≤ × ≤ 1 and y = 0 and 0.5 starting from the metal-oxides and carbonates. The prereacted material was pressed into pellets and sintered in air at 830°C in several steps up to 785 hours. Resistively measured critical temperatures T c (midpoint) between 108K and 114K were achieved for 0.2 ≤ × ≤ 0.5. T c,o and the onset of the transition observed by ac-susceptibility is usually 3K lower. X-ray diffraction studies show that long term annealing is essential for the formation of the 110K high-T c -phase. DC-magnetization measurements exhibit after 143h annealing steps in the Meissner as well as in the shielding signal at 112K and 80K. The 80K features disappear after annealing for 785 hours. The extended levitation of the samples in inhomogeneous magnetic fields after cooling in liquid nitrogen shows that the volume fraction of the 110K phase is very large.

The specific heat C(T) of Bi2Sr2CaCu2O8 was measured at 80 mK ≤ T ≤ 40 K and in magnetic fields up to 8 T. For T ≤ 400 mK, C(T) is well described by C(T) = γ* · T + α/T2. For increasing temperature as well as for increasing magnetic field, the coefficient γ* of the linear term is strongly depressed. This result is interpreted best in terms of spin-glass physics due to a very low (≈ 0.1%) concentration of localized Cu2+ moments, consistent with the absence of any sizeable Curie term in the normal-state magnetic susceptibility.

We report measurements of (i) the DC magnetization of La1.85Sr0.15CuO4 and YBa2Cu3O7, (ii) thermal properties of La2-xSrxCuO4 (x = 0.15) and (iii) transport properties of YBa2Cu3O7. We arrive at the following results: (i) The shielding magnetization of the sintered pellets studied is dominated by inter-grain Josephson contacts, but we find no evidence for additional intra-grain Josephson contacts. (ii) High-Tc superconductivity is a bulk effect. (iii) For YBa2Cu3O7 the effective mass m* of those carriers involved in the superconducting transition is of the order of 4m0.

We report results for the thermal expansion, α(T), of La2CuO4 and La1.85Sr0.15CuO4. Both compounds exhibit surprisingly similar anomalies in α(T) near 36 K. While for the Sr-doped compound this anomaly is shown to indicate bulk superconductivity, for La2CuO4 it has to be attributed to a structural phase transition. Our results suggest that the onset of superconductivity, both in minor parts of the volume in La2CuO4 and in the bulk of La1.85Sr0.15CuO4, is accompanied and possibly even triggered by this structural transition.

Polycrystalline samples of CeCu2Si2 exhibit bulk superconductivity carried by “heavy fermions”. While usually Tc ≊ (0.55 ± 0.15) K, a few samples showed considerably lower transition temperatures (Tc ⩾ 0.11 K), which could, however, be raised to usual values by proper heat treatment. We found that lower Tc's are accompanied by both slightly reduced values of the spin-fluctuation temperature of the Ce3+ ions and the phenomenon of “gapless superconductivity”. In agreement with recent results by Aliev et al. [5], a CeCu2Si2 single crystal did not become superconducting above 20 mK, but showed a 20% deficiency in Cu occupation.

Elastic and inelastic neutron scattering studies of the Kondo lattice CeCu2Ge2 were performed. AtTN=4.1 K an incommensurate magnetic order develops with an ordering wave vectorq0=(0.28, 0.28, 0.54) and an ordered moment µs=0.74 µB. The crystalline electric field splits the 4f1-J-multiplet of the Ce ion into a ground state doublet and a quartet at 191 K. The wave function of the ground state yields an ordered moment of 1.54µB. Thus, due to the onset of the formation of a Kondo singlet the magnetic moment is considerably reduced. The magnetic relaxation rate Λ was investigated via quasielastic neutron scattering. The temperature dependence of Λ(T) is characteristic of heavy-fermion systems with a high temperature square root dependence and a limiting low temperature value, yielding a Kondo temperatureTK≈10K. The quasielastic component of the scattered neutron intensities persists down to the lowest temperatures, well belowTN. This quasielastic line is regarded as a characteristic feature of heavy-fermion systems and corresponds to the enhanced value of the linear term of the specific heat.

We report results on the normal-state (n-state) and the superconducting properties for CeCu2.2Si2 and the quasi-binary alloys Ce1-xMxCu2.2Si2 with M=La (x⩽11 at%) and M=Y(x⩽3 at%). Upon increasing the dopant concentration, the specific heat jump height, ΔC, is depressed much more strongly than Tc. This proves a pair-breaking effect of the La- and Y-induced “Kondo holes” — characterized by temperatures Th, La and Th, Y, that show an anticorrelation to the characteristic temperatures (T∗La, T∗Y) of the underlying Ce1-xMxCu2.2Si2 systems. Compared with La, Y impurities are more efficient in pair breaking and in destroying coherence in the normal state, presumably owing to a less anisotropic scattering potential.

Magnetic, calorimetric and transport measurements characterize CeCu2Ge2 as a Kondo–lattice system which orders antiferromagnetically below TN = (4.15 ± 0.05) K. The low-temperature specific heat shows a magnon-derived T3 term and, in addition, an electronic contribution γ(T)T. γ(T) extrapolates to 0.1 J/K2mol as T → 0 and assumes a large maximum of 0.22 J/K2mol at T = 0.45 K.

Magnetic fluctuations in CeCu2Si2 were directly observed, both above the superconducting transition temperatureTC as well as below. Spatial correlations of the magnetisation density belowTC are weak, resulting in an essentially wavevector independent magnetic response. The intensity observed within an energy window of ±5 THz centred on ω=0 THz corresponds to 1µβ per Ce atom. Higher energy excitations peaking between 7–10 THz were observed and are probably due to higher crystal field levels.

Ce${\mathrm{Cu}}_{2}$${\mathrm{Si}}_{2}$ single crystals prepared with an excess of Cu exhibit low residual resistivity ${\ensuremath{\rho}}_{0}$, low susceptibility $\ensuremath{\chi}$, small unit-cell volume $V$, and bulk "heavy-fermion" superconductivity below 0.65 K, while crystals grown from stoichiometric melt show higher ${\ensuremath{\rho}}_{0}$ and $\ensuremath{\chi}$, larger $V$, but no superconductivity. Ce${\mathrm{Cu}}_{2}$${\mathrm{Si}}_{2}$ behaves as an $s$-state superconductor with strongly temperature-dependent pair breaking and almost isotropic Fermi surface.

We present the results of two types of inelastic neutron scattering experiments on the heavy-fermion system ${\mathrm{CeCu}}_{2\ifmmode\pm\else\textpm\fi{}0.2}$${\mathrm{Si}}_{2}$ to investigate the quasielastic scattering (low-energy response) and the crystal-field (CF) excitations (high-energy response). A characteristic energy width of about 0.7 meV is found for the magnetic low-energy response at low temperatures, and the CF scheme given earlier for ${\mathrm{CeCu}}_{2}$${\mathrm{Si}}_{2}$ is roughly confirmed. The inelastic spectrum of ${\mathrm{CeCu}}_{2.2}$${\mathrm{Si}}_{2}$ gives some indications for a coexistence of \ensuremath{\gamma}-cerium and \ensuremath{\alpha}-cerium. The scattering intensities are compared with static susceptibility measurements.

For the high-Tc superconductor La1.85Sr0.15CuO4, we present results for the low-field magnetization and the lower and upper critical fieldsBc1(T) andBc2(T). ForBc1(0) we find a value of about 20 mT. Extrapolating our resistive data for the transition midpoint taken in fields up to 12 T, we deduce a value of about 50 T forBc2(0). TheBc2 values obtained by inductive measurements are significantly lower. We explain this by a largeBc2 anisotropy due to the layered structure of these compounds. Losses in the Meissner state observed in magnetization and susceptibility measurements disappear after powdering the sample. This is taken as strong evidence for intergrain Josephson coupling in the bulk sample.

An inelastic neutron scattering study is performed on the new magnetically ordered heavy-fermion systems CeCu2Ge2 and CeAg2Ge2. The temperature dependence of the quasielastic line can be interpreted in terms of a Kondo type of behavior. In addition crystalline electric field transition energies are reported.

The magnetic properties of CeCu 2 Si 2 -samples prepared with varying amounts of Cu are compared. The low- T Pauli-susceptibility depends weakly on sample preparation. The Wilson-ratio is 3+ impurities and a large magnetoresistance are observed.

The magnetic relaxation rates Γ as determined via inelastic neutron scattering experiments are reported for the ternary compounds CeM 2 X 2 (M  Ni, Cu, Ag, Au, Ru; X  Si, Ge). Strongly enhanced values of Γ and deviations from a Korringa-type of behaviour were found. A close correlation between the unit cell volume and the 4f-local spin / conduction electron hybridization is demonstrated.

We report results of the specific heat, dc susceptibility, thermal expansion, thermopower and resistivity for a number of Ce(Cu1−xNix)2Ge2 alloy. Upon increasing x, a non-linear increase of the heavy-fermion band width T∗ and a stron non-monotonic Neel temperature TN(x) are found ( T N = 4.1 K for x = 0 and T N K for x ≧ 0.75 ).

The spin relaxation rates Γ in magnetically ordered Kondo lattices have been determined using neutron scattering techniques. Enhanced values of Γ and distinct deviations from a Korringa-type of relaxation behaviour were found. Gaussian contributions to the quasielastic scattered intensities were interpreted as being due to magnetic fluctuations.

Specific heat, resistivity and inelastic neutron scattering experiments are reported, which demonstrate that CeNi 2 Ge 2 exhibits a heavy-fermion groundstate which is neither magnetic nor superconducting. The specific heat coefficient γ( T ) reaches 350 mJ/K 2 mol and exhibits a peak at 0.4 K showing that coherence effects become important at low temperatures. The magnetic relaxation rates as measured via the line width in inelastic neutron scattering experiments are strongly enhanced and deviate from a Korringa law behaviour. The Kondo temperature T K ≈ 30 K was determined from the magnetic relaxation rates and from the specific heat data.

In Ce 1− x Gd x Cu 2.2 Si 2 spin-glass ordering coexists superconductivity below the “critical” ( T c → 0) concentration x cr = 5.1 at %. For samples with slightly lower Gd content, a small volume fraction of ⋍ 10% remains superconducting presumably due to demagnetizing effects. Thus, the full T c ( x ) dependence is accessible. It closely follows the AG-result and proves the existence of a “paramagnetic” pair-breaking mechanism.

We present results for the thermal expansion, α(T), of both polycrystalline and single crystalline La2CuO4. Our results demonstrate the existence of an anomaly in α(T) aroundT=35 K which is clearly intrinsic and most likely due to a lattice instability.

Both, La 2 CuO 4 and La 1·85 ,Sr 0.15 CUO 4 exhibit a bulk phase transition around 36K in the thermal expansion. While in La 1.85 Sr 0.15 CuO 4 this is associated with bulk superconductivity, demonstrated by a Meissner effect of ∼ 13%, the superconducting volume fraction of La 2 CuO 4 amounts to only 10 −4 of the total volume. In La 2 CuO 4 time-dependent phenomena were observed.

Non-magnetic La and Y impurities in CeCu 2.2 Si 2 give rise to a “diamagnetic” pair-breaking effect and, in addition, Gd causes “paramagnetic” pair breaking. In dilute (0 1-x La x Cu 2.2 Si 2 alloys an “alloying-induced depression of incoherent scattering” is observed and related to the formation of antiferromagnetic order at several K.

Preliminary results of the resistivity, dc-susceptibility and specific heat for Ce1−xLaxCu2.2Si2 (0.015

For T 2 Cu 3 O 7−gd (δ = 0.13 and 0.99) can be decomposed into a nuclear term αT −2 and a linear term γT (γ = 20–30 mJ/KZ mole), which is strongly depressed by increasing the temperature as well as the external magnetic field. We attribute the γT term to a spin-glass type freezing mechanism. The large a-value (54 μJ/K mole) found for δ = 0.13 indicates considerable Zeeman splitting of nuclear spin states in the absence of both long-range magnetic order and an external magnetic field.

We present results from electron energy-loss spectroscopy on Nd2−xCexCuO4. There is no clear evidence for Cu1+ but for holes at the oxygen sites. The valency of Ce is found to be close to 3.4. Thus our results do not corroboraten-type superconductivity in this compound.

The thermal expansion, α(T), of a La2CuO4 single crystal, measured along and perpendicular to the [001] axis, is strongly anisotropic. Two α(T) anomalies, presumably of structural origin, show up: A sharp transition at 32 K, frequently accompanied by time-dependent phenomena, is followed by a broad one at 36 K.

For the high-Tc superconductors La1.85Sr0.15CuO4 and YBa2Cu3O7 we present results for the low-field magnetization and the lower and upper critical fields Bc1(T) and Bc2(T). Losses in the Meissner state observed in magnetization and susceptibility measurements disappeared after powdering the sample. This is taken as strong evidence for intergrain Josephson coupling in the bulk sample. The Bc2(T) obtained by inductive measurements indicates a large anisotropy due to the layered structure of these compounds.